Controlling the safe and proper transfer of flammable fluids when loading transportation vehicles such as tanker trucks has long been a concern in the petroleum industry. In recent years, safety devices have been implemented on tanker trucks that prevent fluid transfer from a loading terminal to the truck if certain unsafe conditions surrounding the transfer exist. These devices use detection equipment to determine if all of the safety precautions have been taken and prevent fluid flow if they have not. The electronics systems include overfill detection, grounding and vehicle identification systems. When the vehicle connects to a rack, a sophisticated controller is connected to the truck and the vehicle electronics are monitored. The fluid flow is controlled electrically and can be prevented, by closing a valve in a fluid transfer conduit, or by disabling a pump that is responsible for transferring the fluid to the tanker.
A tanker truck 100, as shown in FIG. 1, has multiple fluid containment compartments 102. The number of compartments can vary from one tanker truck to another. In the United States, tanker trucks typically have four to five compartments, and in Europe, tanker trucks can have up to sixteen compartments. Consequently, each compartment 102 can be filled with a different type of fluid; this provides for the transit of a variety of fluid types in a single truckload. Further, each compartment can have a total volume that differs from one another. Moreover, each compartment can have some remaining fluid, the amount of which can differ from one compartment to another. As a result, the amount of fluid required for filling each compartment 102 can be different.
To prevent overfilling of the compartments 102, an overfill sensor 104 is located in each compartment. In general, the sensor 104 is located near the top of the compartment to detect if the fluid within has reached a certain threshold level. The threshold level can depend on the size of the compartment or on the specific type of fluid that is being transferred into the compartment. The sensor 104 of each compartment 102 is connected to a connection socket 106. A pumping controller 108 is connected to the connection socket 106 via a plug 110. The controller 108 is therefore able to receive the signals from the various sensors on the truck (overfill, ground, etc.) and controls the filling of the tanker truck 100. When a hazardous condition is detected, such as when one of the overfill sensors indicates that the fluid in its compartment has reached the threshold level, the controller 108 will halt the filling process.
There are several types of sensors and various ways of connecting the sensors 104 to the connection socket 106 of the controller 108. For example, one sensor type has two wires and each sensor is independently connected to the connection socket. This provides a relatively simple way for the controller to monitor the sensors because, when a sensor detects an overfill condition, the controller can determine which sensor has been triggered and, therefore, which compartment is full. However, as each sensor is independently connected to the connection socket, a sufficient number of available pins are required on the connection socket for connecting the sensors all at once. This can be particularly problematic for trucks having a larger number of compartments and, therefore, requires a large number of sensors to be connected. The number of pins provided on a standard connection socket, i.e., ten, may not be sufficient.
In another example, an alternate sensor type has a connector with five wires with the overfill sensors connected together in series in a “daisy chain.” That is, a detection signal from a first sensor is passed to a subsequent sensor, and so on, to the end of the sensor chain, the detection signal from the last sensor being returned to the controller. If there is an overfill condition in any one of the compartments, the sensor for that compartment will not output the detection signal, the chain is broken and the controller does not receive the detection signal. The absence of a detection signal at the output of the daisy chain indicates to the controller the presence of an overfill condition in one of the compartments. Irrespective of the number of sensors connected to the controller, the number of pins required by the daisy chained sensors on the connection socket is always the same, so the number of truck compartments that may be monitored is not limited by the socket. However, the monitoring process of the controller is more complex, since it is difficult to identify which of the daisy chained sensors is detecting an overfill condition. Moreover, unlike with the two-wire sensor, malfunctioning sensors can very easily be bypassed, leaving the compartment of the sensor unprotected from possible overfills.
The sensors 104 of the compartments 102 that are daisy chained together are connected so that the output of one sensor is the input of the next sensor. A pulse generator on the controller on the loading terminal sends a pulse to the input of the first sensor 104 and the controller 108 looks for a pulse return at the output of the last sensor 104. If the return pulse is detected, the controller 108 determines that all sensors are connected and that none of the compartments is overfilled. However, if there is no return pulse detected, the controller 108 determines that either at least one sensor is disconnected or that, in at least one compartment, the fluid has reached its overfill level, and therefore terminates the filling process for all compartments.
It is also known to provide a second checking mechanism that uses a an identification module such as the T.I.M.® electronics module from Scully Signal Company of Wilmington, Mass., to assign a unique serial number to a vehicle. The T.I.M. system, once attached to a specific vehicle, associates a unique ID, i.e., a Truck ID (TID) that can be read by several different systems. The TID is used for several purposes by the terminal automation system and rack controller 108.
As known, the T.I.M. system and associated TID can be used to validate a vehicle's authorization to load in an unmanned terminal. In such a system, the rack equipment (or terminal automation system) 108 maintains a list of authorized trucks, by TID, that are approved to load at that loading bay. If an unauthorized vehicle attempts to load, the system denies loading and records the attempt for logging or data collection purposes.
In addition, the TID can be used for verifying fuel type access. Here, a loading rack 108 checks an incoming vehicle's TID to validate that the fuel they are attempting to load is approved for that vehicle. A loading facility often has multiple loading racks, for example, one might be for dispensing diesel fuel, another for gasoline and yet another for aviation fuel as found at a military base or airport. The use of the TID for fuel verification prevents a vehicle from taking on the wrong fuel type.
In the event the truck has a failure of these electronics components it will not be allowed to load and the problem must be troubleshot and the underlying failure resolved. A truck driver, however, might not become aware of this until attempting to load fuel. Thus, a lot of time could be wasted waiting in line only to find out that fuel cannot be taken onboard. There exists, therefore, a need for a way to quickly test the onboard safety equipment on a tanker truck.